Montana Field Guide

The following is taken from Pearson et al. (2015). Body length is 12-14 mm. Mostly various shades of metallic green, olive, dark green to purplish or reddish-green, sometimes black; maculations thick and complete, middle maculation a line curving posteriorly at a sharp angle toward midline and does not reach outer edge of elytra; entirely metallic blue-green below, forehead hairy.

Tiger beetle life cycles fit two general categories. “Spring-fall” beetles emerge as adults in late summer and fall, then overwinter in burrows before emerging again in spring when mature and ready to mate and lay eggs. The life cycle may take 1-4 years. “Summer” beetles emerge as adults in early summer, then mate and lay eggs before dying. The life cycle may take 1-2 years, possibly longer depending on latitude and elevation (Knisley and Schultz 1997, Leonard and Bell 1999). Adults of Cicindela decemnotata decemnotata across range are active from mid-March to July and again in early September to mid-October. At higher elevations from late June to late August (Larochelle and Larivière 2001, Pearson et al. 2015). In Montana, generally early April to June and late August to September (Knisley et al. 2012, Nate Kohler personal communication), May to early July and September to early October in the Centennial Valley (2030 m elevation) of Beaverhead County (Hendricks and Roedel 2001, Hendricks and Lesica 2007, Winton 2010).

The following comes largely from Pearson et al. (2015). Anterior maculations are two dots projecting only slightly toward inner edge of the elytra. In Montana, distinguished from the Green Claybank Tiger Beetle (Cicindela denverensis) and Common Claybank Tiger Beetle (Cicindela limbalis) by the thicker maculations, a middle maculation that does not reach the outer edge of the elytra, the sharp angle at which the middle maculation bends posteriorly with an indistinct foot near the midline, and the undersides entirely metallic blue-green without coppery tones on thorax.

Non-migratory but capable of dispersal. When wings are fully developed (macropterous), a strong flier and fast runner (Larochelle and Larivière 2001).

Adult and larval tiger beetle habitat essentially identical, the larvae live in soil burrows (Knisley and Schultz 1997). Cicindela decemnotata are found in open ground, badlands, stabilized dunes, sparsely vegetated grassland, open pine forest, sagebrush steppe, saline flats and stony shorelines, brushy areas with clay, sand, or gravelly soils. Road cuts, dirt paths, livestock paths (Vaurie 1950, Hooper 1969, Acorn 2001, Larochelle and Larivière 2001, Kritsky and Smith 2005, Hendricks and Lesica 2007, Pearson et al. 2015).

Larval and adult tiger beetles are predaceous. In general, both feed considerably on ants (Wallis 1961, Knisley and Schultz 1997). Diet unreported for Cicindela decemnotata decemnotata but probably mostly small insects and spiders.

Larval tiger beetles live in burrows and molt through three instars to pupation. Adults make shallow burrows in soil for overnight protection, deeper burrows for overwintering. Adults sensitive to heat and light and most active during sunny conditions. Excessive heat during midday on sunny days drives adults to seek shelter among vegetation or in burrows (Wallis 1961, Knisley and Schultz 1997). Cicindela decemnotata decemnotata has a wide range of ecological tolerance (eurytopic). Diurnal, solitary; often sunning on warm soil, attracted to night lights. Predators not reported but likely include robber flies. Escapes by flying quickly and seeking cover in vegetation rather than alighting in open ground. Wary and difficult to approach. Associated tiger beetle species include C. purperea, C. longilabris and C. formosa (Vaurie 1950, Larochelle and Larivière 2001, Hendricks and Lesica 2007) and likely includes others (Kritsky and Smith 2005). Apparently occurs in patchy colonies (Pearson et al. 2015).

Mating reported May to June, duration brief (Larochelle and Larivière 2001). In Montana, mating observed late May to early July (Hendricks and Lesica 2007). Larvae take two years to develop to adults but possibly three years at higher elevations and latitudes (Pearson et al. 2015). Adults emerge in fall and then overwinter (Acorn 2001).

Not considered rare or in need of special conservation management (Knisley et al. 2014). Some colonies (particularly the larval burrows) could be impacted by trampling through livestock overgrazing, but grazing at appropriate times and stocking levels could also be beneficial by keeping vegetation cover more open (Knisley 2011). Prescribed fire may have a local negative impact on abundance for the first year post-burn (Winton 2010) but could be beneficial in creating a mosaic of successional states.